This invention relates to telephone communication equipment and, more particularly, to a compact configuration of circuitry employed in separation of video/data signals and voice signals in the central office of a telephone company (telco) and, more particularly, to an electronically activated bypass of a POTS splitter to enable testing of a DSL line.
Telephonic communication among homes, businesses, and other facilities is accomplished in well-known fashion via one or more central offices of a telephone company with the electrical signals being communicated via pairs (twisted pairs) of electrically conducting wires. Voice signals are transmitted in a frequency band of a few kilohertz (kHz), typically 0-4 kHz, wherein the twisted wire pair can carry signals ranging from DC (direct current) to the high frequency cutoff of the transmission circuitry. For normal voice signal transmission, the high frequency cutoff is in the range of approximately 3-4 kHz. However, the twisted wire pair is capable of transmission of electrical signals of higher frequency, suitable for computer modem digital communication, and for compressed video signals such as video signals transmitted in the MPEG-2 format, wherein a DSL frequency band of 30 kHz to 1104 kHz (kilohertz) is available for these signals. Unlike transmission of such signals by coaxial cable and by satellites wherein the signals are modulated onto carriers, in the transmission of the signals via the twisted wire pair there is no use of a carrier and the signals are transmitted in their baseband format. As a result, there is considerable interest in the use of telephone lines of the telco for communication of high-speed modem signals and compressed video signals in addition to voice signals among the homes, businesses, and other facilities who are the telephone subscribers.
In communication, via the telephone lines, of the combined signals of voice plus video, or other higher frequency signals such as the high speed data transmitted by modem signals, the fidelity of the voice signal is enhanced by separating the voice signal from the high frequency signals. Voice circuitry, such as transmitter and receiver, is employed for handling the voice communication, and DSL (digital subscriber line) circuitry is employed for handling the video and the data. At the telco and at the subscriber premises, the voice and the video are handled separately by the voice and DSL circuits, while between telco and the subscriber premises, both voice and video are communicated by a common twisted pair.
In the telco, a low pass filter is provided for each of the circuits to separate the voice from the DSL so that the voice can be transmitted over long distance lines without interference from the higher frequency signals of the DSL channel. The telco may be provided with numerous racks of cards containing the low-pass filters to provide the splitting of the DSL signals from the voice signals, this portion of the telco being referred to as the POTS splitter. An aspect in the construction of the circuitry at the POTS splitter is the use of a capacitive connection of the DSL line to the voice line to enable the aforementioned twisted pair to carry both the voice and the DSL or video signals from the telco to the subscriber premises, while the capacitive coupling prevents DC on the twisted pair from being communicated to the DSL circuitry.
There are times when it may be necessary to test the integrity of the line carrying the DSL signal through the telco to the subscriber premises. To conduct such a test, it is necessary to provide a DC connection through the POTS splitter. In addition, the test is conducted by injection of a test signal into the DSL line, and measuring reflections of the signal. With presently available equipment, there is an inconvenience in the conduction of such a test because it is necessary to enter the POTS splitter portion of the telco to provide a DC bypass around the capacitors which connect the DSL line to the voice line. This inconvenience represents a problem because of the need for additional personnel and additional time in the conduct of the test procedure.
The aforementioned problem is overcome and other advantages are provided, in accordance with the invention, by a construction of a bypass circuit which bypasses the capacitive connection of a DSL line to a voice line via a DC connection, and wherein the invention provides also for a remote activation of the bypass circuit, so as to enable conduction of the test procedure without requiring personnel to enter into the POTS splitter to handle the numerous racks of circuit cards for effecting the DC bypass during the test procedure. A separate bypass circuit is provided for connection of a DSL line to a voice line.
The bypass is accomplished by means of an electronically activated switch, or relay, which provides a DC path through the POTS splitter from the DSL port to the port which exits to the subscriber premises, the DC path bypassing the terminals of the capacitors which serve to connect the DSL line to the subscriber twisted pair line. Between the DSL signal source and the POTS splitter, there is provided a port for administration of the test signal, and also a port for administration of a bypass-switch activation signal. The invention includes a circuit which detects the switch activation signal, and in response to the switch activation, drives the switch from the normal switch position to the bypass position. The circuit includes a bandpass filter having a passband that selects the activation signal from among other signals which may be present, such as a voice signal or a video signal. The foregoing ports to the DSL line and the switch driver circuit allow personnel to operate from a location outside the POTS splitter to operate the bypass and to conduct a test of the DSL channel.